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El Nino This Winter — Still a Factor?

 

It certainly is true that El Nino has been a long time in coming this year.  Ordinarily, when El Nino events develop, they become well-established by late autumn.  In 2014, there were signs in the early summer that El Nino was quickly forming, but these early signs retreated during the late summer into early fall.

This map shows above normal Sea-Surface temperatures typical of El Nino along the Equator across the Pacific Ocean

This map shows above normal Sea-Surface temperatures typical of El Nino along the Equator in the Pacific Ocean.  (White areas represent land masses of Australia to the lower left and central/South America to the far right.)

 

While some indicators (Sea Surface temperatures) seem to show El Nino developing in recent weeks, others (upper-level winds and the unseasonable November cold) are not characteristic of El Nino.

While it still is more likely than not that we’ll see El Nino develop in the next few weeks, the timing of this event would be unique.  I don’t see any years in which, by typical ways of measuring the starting point, El Nino developed as late as November or December.  So, we’re truly in “uncharted territory” for making the winter forecast!

It is clear that the weather this fall has not followed the pattern of 2009 (an El Nino year which was used to predict our cooler than average summer weather).   El Nino developed by the end of summer in 2009, and October of that year was both cold and wet across southern Minnesota followed by one of the warmest Novembers on record.

I do find five years when El Nino developed rather late (around September) and those would be 1969, 1976, 1977 (perhaps a reinvigoration of the event which started in 1976), 1994, and 2006.  Only one of those five years (1994) had a mild October, and all but 1976 and 1977 had mild November weather, so none of them match this year’s fall weather pattern.  None of the other El Nino years which I have examined went from mild in October to cold in November as we’re almost certain to see in 2014.  In general, I would expect that if El Nino becomes better established through the next couple months, that the coldest winter weather with respect to normal will soon be past, with better prospects for milder than normal conditions as we go through December into early 2015.   For an example of why this expectation could fail, let’s look back at a recent event which was similar to what happened in late autumn of an El Nino year in the late 1970s.

The recent event bearing a striking similarity to late fall of 1977 occurred during the first week of this November.  A very strong Typhoon (named Nuri) developed in the Pacific and the remnants moved toward Alaska on November 8th and 9th.  The storm which resulted threatened the all time record low barometric pressure for Alaska’s Aleutian Islands set in late October of 1977 due to the remnants of another strong Typhoon.  Both of these big Alaskan storms (both in 1977 and this year) helped to build large ridges of high pressure near the West Coast of the United States, and in turn dislodged the type of Arctic air which is now affecting the central United States.  In 1977, cold weather arrived for mid-November, and stayed around for most of the winter.   Though I do not expect a persistently cold winter of 2014-15, this type of typhoon-induced pattern change has kicked off a cold winter at least once before — even with El Nino in place.

October in Review (posted November 2nd)

 

While starting out on the chilly side of normal, October turned exceptionally pleasant.   Among nine days which reached 70 degrees or warmer during October at the Marshall Airport, the 77 degree high on October 24th was 22 degrees warmer than normal, and just five degrees short of the daily record high for Marshall set in 1989.  Temperatures averaged well above normal during the second half of the month until plunging far below freezing on the morning of the 31st and even approaching daily record levels in some areas from Marshall north and west.   Marshall’s Halloween morning low temperature of 17 degrees was just four degrees above the daily record set in 2002. While readers of the Wind Directions Newsletter know that the dry weather experienced during the month was no surprise, the warmth definitely exceeded expectations!  The month ended up ranking among both the top 25 driest and top 35 warmest Octobers for southwest Minnesota since 1895.

The large temperature swings that we saw during the last week of October are typical of fluctuations which occur more commonly during November when the northern branch of the jet stream more often dips southward across Minnesota.  Minor changes in the track of any weak disturbances moving along this jet stream can easily result in temperatures straying 5 to 10 degrees from the expected levels and can also bring sudden changes in the expectations for precipitation type and amounts.    The result is lower confidence in forecasts made for even a three to five day period.

It concerns me that the forecast maps for about November 9th and 10th are showing an upper level pattern reminiscent of last winter, with ridging at the upper levels along the West Coast and an upper-level low north of Minnesota.  So far, no sign of this pattern lasting for more than a couple days, but I will be looking closely for any hints that may indicate whether this chilly-looking  pattern will become commonplace for a second winter in a row.

October so Far – Cool and Dry (posted October 11th)

 

 

Four weeks after an early frost nipped scattered sections of Southwest Minnesota, a more general frost and freeze ended the growing season across the area on the mornings of October 10th and 11th.   Though all reporting stations fell below 32 degrees, the coldest temperatures included 24 degrees at Granite Falls on Friday the 10th, and Saturday morning lows of 27 at Redwood Falls, Windom, and Slayton.   These dates are very close to the normal time of our first hard freeze (28 degrees or colder) in the autumn.  

10-1 to 10-10 DepTempHPRCC-MN

Temperatures of two to three degrees cooler than normal were experienced rather uniformly across Southwest MN during the first ten days of October.

 

Though October has started cooler than normal across the area (see map to left from the High Plains Regional Climate Center), the tendency for temperatures to fluctuate between well above and well below normal may very well repeat during the middle portion of October.   Enjoy the next five mild days which should reach the low to middle 60s.  Following some rain late Sunday and Sunday night (which should total less than 0.25″) excellent harvesting weather is likely for the remaining days through October 18th, helping to reduce the moisture content of standing corn.

 

 

 

This month is on track to join the cool and dry Octobers of 1987, 1991, and 2006 as years when El Nino events started which brought this type of October pattern .  And yes, the Climate Prediction Center experts continue to forecast a 65% or higher probability that El Nino will finally take hold in the Pacific Ocean during the next few weeks. 

 

 

Past Autumn Weather and Winter 2014-15

 

Mid-September Historical Weather Highlights for Minnesota (from Twin Cities National Weather Service)

September 9th

2002: A late-season tornado strikes Albertville just after midnight. It completely tore the roof off of one home. Roofs were partially off a number of other homes, many attached garages collapsed, and a couple of houses were rotated on their foundation. About 20 homes were damaged, nine of which sustained significant damage.

1986: 3 inch hail fell in Watonwan County.

1910: Duluth had the shortest growing season ever with frost free days from June 14 to September 10 (87days). Normally the frost-free season is 143 days.

September 12th

1982: Two tornadoes touched down in Benton County. The F2 tornado caused $250,000 worth of damaged and the F0 caused $25,000.

September 17th

1911: Pipestone is hit with baseball-sized hail that smashes numerous windows at the Calumet Hotel and high school. The local observer measured hail three inches deep. People got their photos taken in automobiles surrounded by the icy white ground.

September 19th

1998: 1 to 1 3/4 inch hail fell in Meeker, Wright, Todd, and Wilkin Counties winds were also estimated over 50kts.

1980: Golfball to baseball sized hail hit St. Paul. One company had 75 to 95 percent of the glass in their greenhouses smashed.

If we look ahead a few weeks, there is a notable trend away from summer and toward winter.  In October, our area is rapidly transitioning from the warm season to the cold season.  Many more of the notable weather events from years past include well below freezing temperatures and early season snowfalls, with progressively fewer occurrences of heat waves or severe thunderstorms.

 

Oct Normal Highs

 

While the normal average highs for the month of October are close to 60 degrees across southern Minnesota, these normals plunge from the pleasant mid to upper 60s during the first few days of October to just above 50 degrees by month’s end.   (Map provided by National Weather Service)

 

 

 

Some mid-October Historical Weather Highlights for Minnesota (from Twin Cities National Weather Service)

October 16th

1937: Snowstorm leaves 10 inches at Bird Island.

1880: Earliest blizzard in Minnesota. Struck western Minnesota and the eastern Dakotas especially hard. Over a foot of snow in western counties. Railroads were blocked. Damage done to Great Lakes shipping. Huge drifts exceeding 20 ft formed in the Canby area lasted until the next spring when flooding occurred across the Minnesota River Valley.

October 17th

1952: Record lows were reported across central Minnesota with lows from 10 to 15 degrees, including a low of 10 degrees at St. Cloud, 12 degrees at Glenwood, and 14 degrees at Alexandria, Litchfield, and Mora.

October 18th

1950: Record high temperatures were set across the area as highs reached the mid to upper 80s. Minneapolis and Farmington saw highs of 87 degrees Fahrenheit, while Albert Lea reached 86 degrees.

October 19th

1972: Cold Snap. 1 above in Tower. 9 in St Peter and Luverne.

1916: Redwood Falls received a record-setting 7 inches of snow.

October 20th

1916: Snow fell in south central Minnesota with 4.5 inches recorded in New Ulm, 4 inches in Farmington and Hutchinson, 3.5 inches in Montevideo, and 3 inches in Faribault.

 

Fall and Winter Outlook

One of our reliable long-range forecast models is predicting a ridge of high pressure aloft to set up farther east than last winter, when it was situated off the U.S. West Coast.   An upper-level ridge of high pressure as forecast over the inland western United States would be associated with above-average winter temperatures especially over western Canada, and below-average temperatures across the south-central and southeastern U.S.  While October and November temperatures in Minnesota haven’t shown a strong trend with this upper-air pattern, mid-winter temperatures have tended to be milder than normal across the northern Plains of the U.S, including most of Minnesota.

The precipitation pattern is not well-defined with the predicted pattern, but the expected development of El Nino for the winter offers what I hope are some reliable clues for predicting the winter pattern.  Of the most recent five winters having the weather pattern expected over the next five months combined with an El Nino event, three landed in the top 20 wettest of the past 120 years.  Three of those five winters also ended up among the top 20 warmest since 1895, and neither of the other two winters was colder than normal.   Because of these historical pieces of evidence, I have moderate confidence in predicting a near to warmer than normal winter, which is likely to bring MORE snow than last winter to Southwest Minnesota.  Last winter’s extreme cold made it easy to overlook that it was the driest winter in Southwest Minnesota since 2007-08, even while east-central Minnesota including the Twin Cities area by contrast had its wettest winter since 2010-11. I would not expect eastern Minnesota to be snowier than last winter, but that area could very well see above normal snowfall again in 2014-15.

Month-by-Month Outlook through February:

October:   Average highs fall from the upper 60s to near 50 by month’s end; average lows begin the month in the lower 40s and fall to near 30 by October 31st.  Precipitation averages about 1.75” for Southwest Minnesota.  Four of the past eight Octobers have been wetter than normal in Southwest Minnesota but individual years have shown some wild swings.  Octobers of 2007 through 2009 were all among the 10 wettest in the past 120 years.  Then we saw a string of three drier than normal Octobers which was snapped in 2013.  There is about a 60% chance that October will end up drier than normal following some unsettled weather in the first couple weeks.  The past two Octobers were a little cooler than normal, and there is about a 75% chance of this October being near to chillier than normal.

November:  Average highs fall to just above the freezing mark by month’s end; average lows begin the month near 30 degrees but fall to the middle teens.  Average precipitation runs about 1.25” for Southwest Minnesota .    This month has been remarkably consistent for warmth and dryness during the past decade.  November across Southwest Minnesota has averaged drier than normal for eight consecutive years, and last November broke a string of 9 consecutive mild Novembers.    Temperatures in those nine mild Novembers (2004 to 2012) averaged 4.3 degrees above the long-term average!   Of the next five months, this appears to be the one with the most uncertain outlook  – in large measure because it’s a time of transition to milder conditions if El Nino takes hold of the winter weather pattern.  Though it’s not as likely as October to be colder than normal, mild November weather is just slightly favored over chillier weather this year.  The precipitation pattern could also go either way (call that a “toss-up”).

December:   Temperatures continue to decline toward the winter lows, and by year end the average high is in the middle 20s with average lows near 5 above.  Average precipitation declines to only about 0.70” for Southwest Minnesota.  If it has seemed in recent years that winter really hits shortly after Thanksgiving, it may be due to the fact that eight of the past nine Decembers have been wetter (usually also whiter) than normal in Southwest Minnesota, with 2011 bringing the lone drier December in that time span.  Last December was the 16th coldest on record and the coldest since 2000.  This is the month with the strongest probability of being milder than normal, and drier than normal weather is also slightly favored.  Only when El Nino was much stronger than expected this winter were both November and December consistently wet across Southwest Minnesota.

January:   The average high hovers in the middle 20s and average lows near 5 above until both begin to rise slightly at month’s end.  Average precipitation is only about 0.60” for Southwest Minnesota.  11 of the past 13 Januaries (with the exceptions being in 2010 and 2011) have been near normal or drier than normal in Southwest Minnesota.   While colder than normal in 2014, January was no colder than February of 2014 and was not quite as cold as the chilly Januaries of 2009, 2010, or 2011.  This was probably due to the limited snowfall last January.

February:    Average temperatures recover with highs just above 32 and lows in the low to middle 10s by month’s end.  Precipitation averages about 0.70” for Southwest Minnesota.  In 2014, this was a dry month averaging about two-thirds of the normal precipitation across the area.  This snapped a five-year string of near to wetter than normal Februaries.  It was the coldest February since 1989, and the 13th coldest in the past 120 years.   Taken together, the first two months of 2015 should have a two in three chance of being warmer than normal, and are nearly as likely (60% chance) to be wetter (and probably snowier) than normal.  However, the expected milder temperatures would result in some of the moisture falling as mixed precipitation or possibly even some rain.

Dry and Cool July – August 4th

July 2014 MN DFN Temps

 

 

While the entire region was cooler than normal during July, some spots along the western and southern edges of Southwest MN averaged as much as 4 to 5 degrees cooler than normal.  (Click on map to view full size)

From Flood to Drought?

In a complete turnaround from June, the “wet” areas of Minnesota have been few and far between so far in July.  Most of Southwest MN has averaged near 25% of the normal rainfall (or about 1.50 inches below normal) through Saturday the 19th.  Soil moisture has now declined to the point that, unless rain falls very soon, prospects will be deteriorating for some crops.

The week ending July 19th averaged about 8 degrees cooler than normal, bringing monthly departures to between three and five degrees below normal across Southwest MN.   The return of cooler than normal temperatures expected for the final weekend of July virtually guarantees our coolest July since 2009.

 

1st half July 2014 MN DFN Temps

 

Dry Spell Now at Three Weeks and Counting – July 14th

 

Though not as dry across the entire area as last week, all areas fell short of weekly normals during the July 7th to 13th time frame.   Cool weather will see us through this week without stressing developing crops too much, but we will really need some better rain as temperatures climb to near and above normal levels by July 20th and beyond.

7 day observed precip to 7-13-14

 

Last Week of Spring Excessively Wet

weekly rainfall to 6-22-14

A few locations south of Marshall received less than 2 inches of rain for the week ending at 7AM June 22nd.  However, amounts in excess of three inches were common across the listening area, and several areas to the northeast of Marshall measured well over 5 inches of rain.

 

Challenges of Forecasting Summer Rainfall

Posted Friday, June 6th —

Last Thursday, June 5th was an occasion when rainfall vastly exceeded forecasted amounts.  Thursday was particularly unique in that unexpectedly heavy rainfall affected the area not once but twice in the same day!  The morning rains developed in an atypical manner (more on that later), while rain had not been expected until much closer to mid-day.  In general, there are several possible causes of summer rains being more or less abundant than forecast.  Any or all of these can produce inaccurate forecasts of rainfall amounts.

  • Warm season rain events have more moisture to draw upon, and may be concentrated in small cells or pockets of intense rainfall.  This can produce an “all or nothing” type effect in which there can be a fine line between heavy rain and mere sprinkles, both in time and distance.
  • Formation of storms may occur at the boundary of warm, humid air and cooler “outflow” remaining from earlier storms.  These boundaries are often either undetected or handled poorly by the major forecast models. This effect definitely enhanced the strength of Thursday’s late afternoon thunderstorms.
  • Forecaster experience may not help overcome the lack of help from the forecast models, because a weather pattern which usually produces little to no rain may produce heavy rain in a small fraction of events.

Specifically, I have identified a handful of reasons that Thursday’s rains were unusual.

  • TIMING – Overnight storms typically die out around sunrise.  These storms developed just after sunrise.
  • SHORT-TERM MODELS had forecast the morning rains to stay to the north of the area.
  • OTHER STORMS were occurring at the same time over Arkansas and Missouri.  These often would have limited the moisture inflow needed to support heavy rainfall in southwest MN.
  • UPPER-LEVEL SUPPORT for the storms was weakening during the day.

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